African humid period

The African humid period was a climate period in Africa during the late Pleistocene and Holocene geologic epochs, when North Africa was wetter than it is today. The covering of much of the Sahara by grasses, trees, and lakes was caused by changes in the Earth's axial tilt, changes in vegetation and dust in the Sahara which strengthened the African monsoon, and increased greenhouse gases. During the preceding Last Glacial Maximum, the Sahara contained extensive dune fields and was mostly uninhabited. It was much larger than it is today, and its lakes and rivers, such as Lake Victoria and the White Nile, were either dry or at low levels. The humid period began about 14,600–14,500 years ago at the end of Heinrich event 1, simultaneously with the Bølling–Allerød warming. Rivers and lakes such as Lake Chad formed or expanded, glaciers grew on Mount Kilimanjaro, and the Sahara retreated. Two major dry fluctuations occurred during the Younger Dryas and the short 8.2 kiloyear event. The African humid period ended 6,000–5,000 years ago during the Piora Oscillation cold period. While some evidence points to an end 5,500 years ago in the Sahel, Arabia, and East Africa, the end of the period appears to have occurred in several steps, such as the 4.2-kiloyear event.